Conventionally, a motor control apparatus of this type includes a motor control apparatus described in PTL 1. FIG. 10 is a block diagram showing a structure of the motor control apparatus described in PTL 1.
Conventional motor control apparatus 50 shown in FIG. 10 is connected to motor 11 and speed detector 13. Load 12 is linked to motor 11. Moreover, speed detector 13 detects a rotating speed of motor 11 and outputs speed detection signal Vd indicative of the detected rotating speed.
Motor control apparatus 50 has a speed control system for causing speed detection signal Vd to follow command speed signal Vr. Motor control apparatus 50 includes first notch filter 15 as shown in FIG. 10 in order to suppress an oscillation caused by machine resonance or the like. Furthermore, motor control apparatus 50 includes speed control portion 14, torque control portion 16, oscillation extracting filter 17, second notch filter 18, and notch control portion 19.
Speed control portion 14 inputs command speed signal Vr and speed detection signal Vd and generates torque command signal τ1. First notch filter 15 serves to apply sharp attenuation to a signal having a frequency within a predetermined range around a specific frequency contained in a supplied signal from the same signal. The frequency to be the center is referred to as a notch center frequency, a vicinal frequency range to be attenuated is referred to as a notch width, and a degree of the attenuation to be applied at the notch center frequency is referred to as a notch depth. Moreover, a frequency specified by the notch center frequency and the notch width is referred to as a notch frequency. First notch filter 15 has such a characteristic and attenuates a signal component of the notch frequency with respect to torque command signal τ1 and supplies, to torque control portion 16, torque command signal τ2 subjected to filter processing. Torque control portion 16 controls motor 11 in such a manner that motor 11 outputs a target torque based on torque command signal τ2 which is input.
Moreover, oscillation extracting filter 17 extracts an oscillation caused by machine resonance from speed detection signal Vd and outputs the oscillation as extracting oscillation signal x1. Extracting oscillation signal x1 is input to second notch filter 18. Second notch filter 18 carries out such filter processing as to attenuate the signal component of the notch frequency over extracting oscillation signal x1 depending on the control of notch control portion 19. Second notch filter 18 outputs second notch filter output signal x2 as the extracting oscillation signal subjected to the filter processing. Notch control portion 19 generates notch frequency set value cn1 based on extracting oscillation signal x1 and second notch filter output signal x2. Notch control portion 19 controls first notch filter 15 and second notch filter 18 based on notch frequency set value cn1 in such a manner that the notch frequencies of first notch filter 15 and second notch filter 18 are equivalent to an oscillation frequency of extracting oscillation signal x1.
In first notch filter 15, a notch depth in the notch frequency has a fixed value. In second notch filter 18, moreover, a notch depth in a notch frequency is represented by −∞.
In the conventional motor control apparatus having such a structure, the notch frequencies of first notch filter 15 and second notch filter 18 are successively changed in such a manner that an oscillation component generated by an oscillation caused by machine resonance for some reason is decreased if any.
Moreover, another example of the conventional motor control apparatus is described in PTL 2. FIG. 11 is a block diagram showing a structure of the conventional motor control apparatus described in PTL 2.
The motor control apparatus shown in FIG. 11 includes notch filter 15b, notch frequency deciding portion 41, adaptive calculating portion 42, and filter coefficient setting portion 43. In notch filter 15b, a notch center frequency is fixed to notch frequency ωn by notch frequency deciding portion 41. On the other hand, a notch depth and a notch width are variable, and the notch depth and the notch width of notch filter 15b are decided based on filter coefficients ξ1 and ξ2 output from filter coefficient setting portion 43.
Adaptive calculating portion 42 successively changes adaptive input ξ in accordance with adaptive law based on output τ2 of notch filter 15b and reference signal u, and outputs the changed input. Filter coefficient setting portion 43 outputs filter coefficients ξ1 and ξ2 indicative of the notch depth and the notch width in notch filter 15b based on adaptive input ξ which is input.
In the conventional motor control apparatus shown in FIG. 11, the notch depth of notch filter 15b is successively changed in such a manner that an oscillation component of an oscillation caused by machine resonance is decreased when the oscillation is caused.
As in PTL 1, however, the notch depth does not take an optimum value in first notch filter 15 having the notch depth fixed. For this reason, there is a problem in that an oscillation is unnecessarily suppressed and a phase delay is thus increased depending on a control target, resulting in an insufficient increase in a control system gain.
As in PTL 2, moreover, there is fear that an oscillation caused by machine resonance or the like might not be sufficiently suppressed in the case in which a variation or aging in a characteristic of a machine, a deviation of a fixed notch frequency from a resonance frequency or the like occurs in notch filter 15b having the notch frequency fixed.
PTL 1: Unexamined Japanese Patent Publication No. 2004-274976
PTL 2: Unexamined Japanese Patent Publication No. 2007-293571